There is generally known a screen printer of a configuration in which a printed wiring board set on a stage is superimposed on a mask sheet and paste, such as cream solder and conductive paste, supplied on the mask sheet is applied (printed) on the printed wiring board at predetermined positions via openings made in the mask sheet by pressing the paste using squeegees.
As is described, for example, in Japanese Patent No. 2682145, a printer of this type is provided with a mask recognition camera mounted to point upward on a movable stage that supports a printed wiring board and takes an image of marks provided on the mask sheet using the mask recognition camera, while it is provided with a board recognition camera provided fixedly to point downward onto the device frame and takes an image of marks on the printed wiring board by allowing the stage to move below the board recognition camera. By checking the relative positional relation of the mask sheet and the printed wiring board on the basis of these images and performing the position matching between the mask sheet and the board, the printed wiring board is superimposed on the mask sheet precisely.
The conventional printer as above executes mark recognition on the printed wiring board (acquisition of printed wiring board position information) for each printed wiring board to be processed, whereas it executes mark recognition on the mask sheet (acquisition of mask position information) only when the mask sheet is attached to the device. This configuration is adopted on the assumption that the position of the mask sheet will not vary.
However, even without any variance in position of the mask sheet, the device as described in the cited reference has a possibility that a travel error (an error from a theoretical amount of travel) occurs in the stage with time due to thermal expansion induced in the drive mechanism while it drives the stage. Accordingly, in a case where printed wiring boards of the same type are produced continuously over a long period, when the position matching between the mask sheet and the printed wiring board is performed according to mask position information acquired through the imaging using the mask recognition camera mounted onto the stage immediately after the production is started and before a travel error occurs in the stage, and printed wiring board position information acquired through the imaging of a printed wiring board W held at the stage using the stationary camera (board recognition camera) after a travel error occurred with an elapse of considerable time for production, there is a displacement comparable to the travel error between the mask sheet and the printed wiring board and print misalignment may possibly occur with time. The prior art, therefore, is susceptible to improvement in this regard.